Percentage computation aid



May 2, wg@ J. R. SEARS 506,390

PERCENTAGE COMPUTATION AID'- APPARATUS Filed Jan. 27, 1947 5Sheets-Sheet l EH (y Gttorneg S May 2, i950 J. n. SEARS 2,5@'gn`;

PERCENTAGE COMPUTATION AID APPARATUS Filed Jan. 27, 1947 5 sheetS-shet 2i@ Llull.

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Mayv 2, 1950 J. R. SEARS 295%939@ PERCENTAGE COMPUTATION AID APPARATUSFiled Jan. 27,1947 5 Sheets-Shree?, 5

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bte/magg Maf; 2, 1950 J. R. SEARS PERGENTGE COMPUTATION AID APPARATUS 5Sheets-Sheet Filed Janv. 27, 1947 Syvum/MM @Him/AWS `N b N MN BNN May 2,1950 J. R. SEARS PERCENTAGE COMPUTATION AID APPARATUS 5 Sheets-Sheet 5Filed Jan. 27, 1947 @w @m y abbo/MMS Patented May 2, 1950 PERCENTAGEooMPU'rATIoN AID ArPARATUs John 1i... Scars, N Orfolk, Va. .applicationJanuary 27, 1947, Serial No. 724,616 13 Claims. (C1. 5235-787) Thisinvention relates to percentage aid coinputation apparatus, and moreparticularly to apparatus for co-relatively positioning` tables orcolumns of numerical values in such manner that percentages of principalvalues at varying percent rates may easily be determined. The inventionmay be embodied in apparatus of the general class referred to in whichpercentages are tabulated in columns on rotatable drums or cylinders.

An objects of the invention is to provide an apparatus of the characterstated which, for a given capacity as to the range oi computations, ismore compact than apparatus previously provided for the same use. Inattaining this object, I provide, in general, two apparatus groups orsections for determining percentages of primary and secondary parts of aprincipal value, based on a selected percent rate, together with meansor markings for co-relating the thus determined percentages andrendering them corelatively readable and distinguishable frompercentages oi the principal sum based on other and non-selected percentrates.

Another object of the invention is to provide a percentage computationaid apparatus including two coaxial, rotatable cylinders mounted torotate independently of each other without any tendency of one cylinderto rotate the other cylinder.

Another object of the invention is to provide apparatus of the kindreferred to including a simple and electve arrangement for mountingbands or rings marked with percentage values on a cylinder or drum.

Other objects will become apparent from a reading of the followingdescription, the appended claims, and the accompanying drawings, inwhich:

Figure 1 is a front elevational View of a simple form of apparatusembodying the invention;

Figure 2 is a longitudinal sectional view of the apparatus shown inFigure l, but with some parts omitted;

Figure 3 is a detail end elevational view of a cylinder and band,illustrating the arrangement for maintaining the band in a predeterminedcircumferential setting or position on the cylinder;

Figure 4 is a detail View showing a group of alternative percent ratemarkings which may be used in place of percent rate markings shown inFigure 1;

Figure 5 is a perspective view illustrating a casing or housing forenclosing apparatus of the kind shown in Figures l to 4;

Figure 6 is a iront elevational view of a modified embodiment of theinventionj Figure 7 is a fragmentary vertical section on the line 'I 'Iof Figure 6; and

Figure 8 is a fragmentary section on the line 3-8 oi Figure 7.

Figures l to 3 inclusive illustrate a simple and preferred iorm or"apparatus adapted to be used as an aid in computing percentages,particularly for computing` interest in banks, building loan associationoces, and other establishments in which interest on diiierent principalamounts and at different interest rates has to be computed as part oithe daily work.

The apparatus shown in Figures l to 3, considered in its general nature,includes a support or stand A on which are mounted two independentlyrotatable cylinder member B and B disposed with their inner ends inface-to-face relationship behind an opaque shield generally designated Cfixed to the support A by a bracket l. The shield C is shown ascomprising a single structural part, but considered functionally itcomprises two inclicating sections,v one designated 2 between thevertical center line of the apparatus and the left end of the shield,and the other designated between the vertical center line and the rightend of the shield as viewed in Figure l.

The shield indicating section 2 is formed with a principal valuedesignation part 3 iormed with a window #3, and is provided with aseries of horizontally aligned percent rate markings 5, 6, 7, 8, 9, and19. The procent rate markings may be changed according to thecomputations to be made. The markings shown in Figure l are respectivelyin descending progression 6%, 51/2%, 5%, l1/2%, 4%, and 3%. rEhe shieldindicating section E! is similar to the indicating section 2 andincludes a primary value designation part 3 formed with a window b3', aswell as percent rate markings 5', 6', 7', 8', 9', and l0 which are thesaine as to value and progression as the percent rate markings 5 to 10inclu ive on the section i?.

The cylinder B is provided with an column l! of primary principal valueindicia located at the left end ci the cylinder so to be behind the'principal value designation 3 of the shield section 2. The calumn il isii th principal values increased 1G@ units between each two adjacentvalue indicia up to ten thousand. The lcylinder B also is provided withannular columns l2, i3, i4, i5, .1.- primary percentage indicia. Thesecolumns are on the cylinder B to be disposed behind the percent ratemarkings 5, G, 7,8, 9, and l0 on the shield 'section 2. is formed with aplurality oi 20, 2 l, 22, and 23 arranged in stepped relationship withthe respective view openings being disposed directly under, that isaligned transversely with the respective percent rate markings 5, 6, 7,8, 9, and l0.

The cylinder B can be rotated by means of a knob device 24 attached tothe cylinder in a manner to be described hereinafter. By rotating thecylinder, any selected principal value in the column l l can be made toregister with the window 4. The primary percentages listed in thecolumns l2, i3, i4, l5, i6, and il are such that when a selectedprincipal value registers with the opening 4 the correct percentage willbe displayed in the view opening directly below the percent rate markingused in the computation. For example, if it is desired to determine theinterest on $8,600 at 6% for one month, the cylinder B is turned untilthe principal value $8,600 registers with the window 4, and thepercentage or interest displayed through the view opening l directlyunder the 6% marking 5 is seen to be $43.00. If it is desired to iindthe interest on $8,600 for one month at 51/2%, the reading of theinterest is made through the view opening I9 directly under the 51/2%marking 6, and is found to be $39.42. Similarly, the interest orpercentage at the rates shown in the markings 7, 8, 9, and 10 can beread easily through the openings 20, 2|, 22, and 23, respectively.

The cylinder B' is provided or marked with an annular column il ofsecondary principal value indicia increasing by ones or units up to$100. The cylinder B' also is marked or provided with annular columns ofpercentage indicia designated 12', 13', 14', 15', 16', and 17' disposedrespectively behind the percent rate markings 5', 6', 7', 8', 9', andl0. The shield section 2 is formed with stepped view openings i8', I9',20', 2|', 22', and 23' respectively aligned directly under the percentrate markings 5', 6', 7', 8', 9', and The view openings in the shieldindicating section 2' are arranged in stepped relationship similarly tothe view openings in the shield section 2, that is, the uppermostopening I8' in the shield section 2' is aligned horizontally with theuppermost opening I8 in the shield section 2, and both openings I8 andI8' are disposed under the 6% markings. Similarly, the immediately loweropenings i9 and IS are horizontally aligned with each other, and aredisposed under the 51/2% sign markings, and so on. The percentagecolumns l2 to Il inclusive are so constituted that when the cylinder B'has been turned by means of a knob device 2li to bring a selectedsecondary principal value into registration with the window 4', thepercentage sought will be found displayed in the view opening disposedunder the marking displaying the percent rate use in the computation.Thus, if it is desired to nd the interest on a secondary principal valueof $44 for one month at"6%, the cylinder B' is rotated to bring thevalue $44 in the column Il' into registration with the window Il'. Theinterest will be observed in the view opening I8' aligned with the sixpercent sign marking 5', and will be seen to be $0.22.

One of the advantages of a construction embodying the invention andincluding the two cylinders B and B in combination with the two shieldsections 2 and 2 marked as described above is that the apparatus can bebuilt comp-actly to occupy a small space and still have the capacity forcomputing percentages at varying rates on a large number of principalvalues. Thus, in the '(5 form shown, the cylinders need be of a diameteronly great enough to permit the inclusion of onehundred items in eachcolumn, which does not require a cylinder of great circumference, butstill permits the nding of percentages on values varying by ones up toten thousand. For example, in nding the interest on $8,644, for onemonth at 6%, the cylinder B would be set to cause the primary principalvalue $8,600 to register with the window 4, and the interest on theprimary value would be observed through the view opening i8 as being$43.00. rIhen the cylinder B would be positioned tocause the secondaryvalue $44 to register with the opening 4', and the secondary interestwould be observed through the window i6' as being $0.22. By a simpleaddition, the interest on the whole sum of $8,644 would be determined as$43.22. It is apparent that if the two cylinders B and B' and theassociated shield sections were not used in combination, only a singlecylinder and shield section being employed, it would be necessary forthe columns on the single cylinder to include ten thousand items,requiring a very large circumference and prohibitively large apparatus.

In accordance with a further feature of the invention, the shield C isprovided, formed, or marked to facilitate the reading of the relatedprimary and secondary percentages in the proper View openings. In theform shown in Figure l, the shield C is marked with guide lines 20, 26,2l, 26, 29, and 30 which extend respectively between and denotehorizontally aligned pairs of view openings in the respective shieldsections 2 and 2'. Thus, the guide line 25 extends between thehorizontally aligned view openings i3 and i6', both of which aredisposed under the 6% markings; the guide line 26 extends between theview openings i0 and i9' both of which are disposed under the 515%markings; and so on. In finding both the primary `and secondarypercentages of a given number, say $8,644, the cylinders B and B' arepositioned as previously explained and the primary percentage-$43.00-isread through the opening i3 under the 6% marking; but instead orlocating the secondary opening i3' by reference to the percent marking5' above it, the operator's eye follows across the guide line 25, whichvisually pairs the opening l0 with the opening i8. The guide line 25serves in a sense to couple the openings i3 and l0' which are associatedrespectively with the primary and secondary percentages under similarpercent rate markings. In the same way, the guide lines 26, 2, 23, 29,and 30 visually couple other associated pairs o1 view openings so as tofacilitate substantially simultaneous reading oi related primary andsecondary percentages determined at equal percent rates.

In using the apparatus, it is desirable to operate both cylinders fromone side, usually the left side, in order that the operators right handmay be free for making written notes. The apparatus shown in Figures 1and 2 is so constructed as to provide this advantage and the particularconstruction is such that it provides the further advantage that turningof either of the cylinders B-B' will not tend to turn the other cylinderand move it from its previous setting. In other words, the arrangementis such that if the cylinder B is rst set to cause a selected principalvalue to be displayed through the window il, the cylinder B' may beturned thereafter to cause a selected secondary principal value toregister with the window 4' without producing any tendency yto turn ordrag the cylinder B from its previously set position. For obtainingthese desirable advantages, the cylinders B and B are mounted on thesupport A by a novel construction shown in Figure 2. This constructionincludes a hub 3l which is integral with the support A and is bored toreceive a sleeve 32, the opposite ends of which protrude from the hub 3lyand provide bearing portions shown at 33 and 33. The sleeve may belocked or secured in xed relationship to the hub 3l by any suitablemeans, for example, by set screws 34-34. The cylinders B and B areformed with hubs 35 and 35 journalled respectively on the bearingportions 33 and 33', so that the cylinders are mounted independently onthe sleeve 32 and do not touch each other. The knob 2d for turning thecylinder B is secured to the outer and left hand end of the cylinder Bby any suitable means, such as screws 36. The knob 2st for turning thecylinder B is, as stated before, located at the same side of theapparatus as the knob 2li. In order to connect the knob 2d' with thecylinder B without causing contacting of any parts which would cause onecylinder to tend to follow the other in rotation, the knob 24 is formedwith an axial opening 3l into which extends, with ample clearance, ashank 33 on the knob 24. The shank 38 is screwed to the which extendsthrough the sleeve 32, the knob 24 being locked to the rod 39 by meansof a screw 49. The right end of the rod 39 is attached by a screw 4l toa non-circular part 42 fitted in a similarly shaped recess 43 in thecylinder B.

It will be seen that the group of parts comprising the knob 24', the rod39, and the cylinder B has no operative or contacting connection withthe group of parts comprising the knob 24; and the cylinder B. There ispositive clearance between the groups ci parts, and consequently eitherknob and the parts connected to it can be turned to rotate theassociated cylinder without producing any tendency to rotate the othercylinder.

Preferably, the percent rate markings 5 to 10 inclusive and 5 to 10inclusive are interchangeable with other percent rate markings,according to the computations to be made. The markings may be changed inany desired manner, as for example, by using replaceable orinterchangeable tabs or labels or by writing in different percent rates.Figure 4 shows a Set of percent rates which could be substituted forthose shown in Figure 1. The percent rates shown in Figure 4 are allbased on six percent but they progress according to the number of monthsfor which interest is to be computed.

When a dinerent set or series of percent rate markings used, it usuallywill be necessary to change the columns of percentages 12 to 17inclusive and 12 to 17" inclusive. In order that this change may be madereadily, the columns of percentage values preferably are marked onremovable rings or bands 44 (see. Figure 3) adapted to be slipped on andon the cylinders B and B in an axial direction. Similarly replaceablebands or rings 44 marked with difiere-nt columns of principal values maybe employed. The bands or the cylinders, or both are provided with meansfor maintaining the bands in predeterminedr positions circumferentiallywith respect to the cylinders. In the constructionv shown in Figure 3,the bands vare formed with internal corrugations i5 adapted to mate withsimilarly formed corrugations 46 on the cylinder- B. Thecylinder B maybe formed with, similar corrugationsadapted to left end of a rod 3S'with the cylindersv B and B mate with internal corrugations of theassociated bands.

Figures l to 4 show a percentage computation aid apparatus of simpleform comprising a minimum number of parts. The construction describedmay easily be mounted in a casing or housing D as shown in Figure 5.Only a few reference characters have been applied to Figure 5 toindicate generally parts which correspond to parts of the constructionshown in Figures 1 to 4 inclusive.

In order that the cylinders B and B may be held against axial shiftingon the sleeve 32, means are provided for coupling the cylinders to thehub 3l of the standard A. The hub 35 of the cylinder B is formed with agroove 41 adjacent its tapering inner end portion 43. The groove 4lreceives a stud 49 carried by a spring nger 5d secured to the hub 3| bya screw 5l. When the parts are in the assembled relationship shown inFigure 2, the stud 49 cooperates with the sides of the groove 4? tomaintain the cylinder Bgagainst axial shifting. However, the cylinder Bmay be removed by forcing it axially toward the left, which will causethe spring finger 50 to yield, permitting the stud 4S to rise out of thegroove 41 and allow the cyliner hub 35 to move axially to the left. Whenthe cylinder B is to be set in its operative position, it is placed onthe sleeve 32 and pushed to the right, causing the tapered edge 4S tolift the stud 49 against the urge or the spring iinger 5l). Upon furthermovement of the cylinder B, the stud 49 will drop into place in thegroove 47. Similarly, the hum 35 of the cylinder B' is formed with agroove 41 which receives a stud 49 carried by a spring finger 56 securedto the hub 3l by a screw 5 l Figures 6 to 8 illustrate a modifiedembodiment of the apparatus including a movably mounted opaque screen Eadapted to be set in diierent positions for obstructing or cutting offview through the openings lt to 23 inclusive and i8 to 23' inclusive,with the exception of two selected horizontally aligned View openingsrelated to equal percent rate markings. Broadly considered, the movablescreen aids in the reading of primary and secondary percentages in muchthe same manner as the guide lines 25 to 9i) inclusive shown in Figurel. Consequently, the guide lines may be omittedfrom the shield C in theconstruction shown in Figures 6 to 8. The shield C shown in themodication differs from that shown in Figure 1 also in that it isprovided with a slot 52 and an additional bracket 53 for assisting thebracket i in. supporting the shield on the standard A. Otherwise theparts shown in Figures 6 to 8 inclusive, with the exception of thescreen E and the parts which mount it, are the same as parts shown inFigures 1 to 3 inclusive and are designated by corresponding referencecharacters.

The screen E is shaped to conform to the surface of a cylinder and ismounted concentrically and the shield C. The screen may be mountedeither inside or outside of the shield C, since in either case, thescreen can obstruct the view of percentage values on the cylinders B andB. In the form shown, the screen E' is disposed between the cylindersB-B' and the shield C, that is, the screen E is mounted behind theshield C.

The screen is provided with twofmounting arms 54v and 55 which merge atinner ends with a ilat hub 56v snugly mounted in a slot 5'! formed in'thel hub Y3l of the standard A. The at hub 56 is journalled on the ixedsleeve 32 and has its opposed ilat surfaces crimped or otherwise formedor equipped to provide for frictional engagement of the hub faces withthe sides of the slot l to hold the screen E frictionally but releasablyin set position. The screen E is rockable about the sleeve 32, and inorder that it may move high enough, it is formed with a slot 58 throughwhich the shield mounting bracket 53 extends. A button 59, secured tothe screen E and extending freely through the slot 52 in the shield C,provides for convenient manual raising and lowering lof the screen.

For rendering two selected horizontally aligned view openings in theshield C co-relatively functional, the screen E is formed with twoelongated horizontal slots 60 and Se', which in eiect constitute asingle slot means extending substantially across the screen. When it isdesired to determine the percentage of say $8,644 at six percent ior onemonth, the knobs 24 and 24 are operated to turn the drums B and B untilthe primary Secondary principal values $8,600 and $44 registerrespectively with the windows il and in the shield C. Then the button 59is moved to rock the screen E to a position in which the slots Et and60' are disposed directly under the view openings l8 and I8'. Theprimary and secondary percentages will then appear respectively in theI,

Windows i8 and I8 as $43.00, and $0.22. With the screen E positioned asdescribed, the opaque portion of the screen, that is the part of thescreen other than the slots 60 and 50', will obstruct view through theopenings i9 to 23 and I9 or 23' so that the only percentages viewablethrough the shield C and screen E are those determined at the 6% ratewhich are to be found.

If it should be desired to iind the percentage or interest on $8,644 forone month at five and one half percent, the screen is removed downwardlyto cause the slots 60 and Gi to register with the view openings i9 andI9', all the other view openings then being cut oi or renderednoniunctional. By shifting the screen E to other positions, the primaryand secondary percentages can readily be determined on the basis of anyselected interest rate.

The constructions illustrated by way of example embody the invention inpreferred forms but it will be understood that changes may be madewithout departing from the invention as defined in the claims.

I claim:

l. In a percentage computation aid apparatus, a support; a relativelyilxed shield having two indicating sections; a first rotatable memberprovided with indicia, individual items of which each represents aprimary part of a principal value and are adap-ted to be denotedselectively by one of said indicating sections according to the rotatedposition of said member; a second rotatable member provided withindicia, individual items of which each represents the secondary part ofa principal value and are adapted to be denoted selectively by the otherof said indicating sections according to the rotated position of saidsecond member; means mounting said rotatable members on said supportindependently of each other with their inner ends in mutual face-to-facerelationship for rotation about a common axis and with each of saidmembers being free to rotate without tending to rotate the other of saidmembers; a first manually operable device connected to the cuter end ofone of said members for rotating it a second manually operable device atthe same end of said one of said members; means operatively connectingsaid second manually operable device to the other of said members forrotating it, said second manually operable device and said connectingmeans being free of connection to said first manually operable deviceand said one of said members, whereby either manually operable devicemay be operated to rotate the member connected thereto without producingany tendency to rotate the other member, and means cooperating with therespective indicating sections of said shield to facilitate thecollective relating of selected markings on the two cooperating members.

2. In a percentage computation aid apparatus, a support; a relativelyxed shield having two indicating sections; a first rotatable memberprovided with indicia, individual items of which each represents aprimary part of a principal value and are adapted to be denotedselectively by one of said indicating sections according to the rotatedposition of said member; a second rotatable member provided withindicia, individual items of which each represents the secondary part ofa principal value and are adapted to be denoted selectively by the otherof said indicating sections according to the rotated position of saidsecond member; a sleeve carried by said support and having end portionsprotruding oppositely from said support to provide axially spacedbearing portions on which said members are journalled respectively withtheir inner ends in face-to-face relationship; a rst manually operabledevice connected to the outer end of one of said members for turning itand having an axial opening coaxial with said sleeve; a rod connected tothe outer end of the other of said members and extending through saidsleeve and said opening; a second manually operable device on said rodand adjacent said first manually operable device, said second manuallyoperable device, said rod, and the one of said members to which the rodis connected being completely free of connection to said i'lrst manuallyoperable device and the member to which it is connected, and meanscooperating with the respective indicating sections of said shield tofacilitate the collective relating of selected markings on the twocooperating members.

3. In a percentage computation aid apparatus, a support; a relativelyxed shield having two indicating sections; a first rotatable memberprovided with indicia, individual items oi which each represents aprimary part of a principal value and are adapted to be denotedselectively by one of said indicating sections according to the rotatedposition of said members; a second rotatable member provided withindicia, individual items of which each represents the secondary part ofa principal value and are adapted to be denoted selectively by the otherof said indicating sections according to the rotated position of saidsecond member; a sleeve carried by said support and having end portionsprotruding oppositely from said support to provide axially spacedbearing portions on which said members are journalled respectively withtheir inner ends in face-to-face relationship; a rst operating knobsecured to the outer end of one of said members and having an axialopening coaxial with said sleeve; a rod secured to the outer end of theother of said members and extending through said sleeve and into saidopening; la second operating knob secured to said rod and being locatedadjacent said rst operating knob, there being positive clearance betweenthe group of parts including said iirst operating knob and theassociated rotatable member and the group of parts comprising saidsecond operating device, said rod, and the associated rotatable member,and means cooperating with the respective indicating sections of saidshield to facilitate the collective relating of selected markings on thetwo cooperating members.

4. In a percentage computation aid apparatus, a shield comprising twoadjacent indicating sections, each section being marked with a series ofprogressively varying percent rates and having a principal valuedesignation part and a series of individual view openings alignedrespectively with the percent rate markings, said openings being in steparrangement, the percent rate markings on said two sections being thesame as to values and progression and the step arrangement of the viewopenings in said two sections being similar; guide lines on said shieldextending respectively between and denoting two View openings in therespective sections aligned with equal percent rate markings; a iirstmember mounted to move behind one of said indicating sections and beingmarked with a column of primary principal values adapted to registerwith the principal value designation part of said one of said indicatingsections, and being also marked with columns of primary percentages ofsaid primary principal values adapted to be displayed through theopenings aligned with the percent rate markings on said one of saidshield sections; and a second member mounted to move behind the other ofsaid indicating sections and being marked with a column of secondaryprincipal values and being also marked with columns of secondarypercentages of said secondary principal values adapted to be displayedthrough the openings aligned with the percent rate markings on saidother of said indicating sections.

5. In a percentage computation aid apparatus, a shield comprising twoadjacent indicating sections, each section being marked with a series ofaligned progressively varying percent rates and having a principal valuedesignation part and a series oi individual view openings alignedrespectively with the percent rate markings transversely to thealignment of the markings of said series, said openings being in steparrangement and at progressively varying distances from the percent ratemarkings with which they are respectively aligned, the percent ratemarkings on said two sections being the same as to values andprogression and the step arrangement of the View openings in said twosections being similar; guide lines on said shield extendingrespectively between and denoting two view openings in the respectivesections aligned with equal percent rate markings; a first membermounted to move behind one of said indicating sections and being markedwith a column of primary principal values adapted to register with theprincipal value designation part of said one of said indicatingsections, and being also marl-ed with columns of primary percentages ofsaid primary principal values adapted to be displayed through theopenings aligned with the percent rate markings on said one or saidshield sections; and a second member mounted to move behind the other ofsaid indicating sections and being marked with a column of secondaryprincipal values and being also marked with columns of secondarypercentages oi said secondary principal values adapted to be displayedthrough the openings aligned with the percent rate markings on saidother of said indicating sections, all of said columns extendingtransversely to said series of aligned percent rates.

6. In a percentage computation aid apparatus, a shield comprising twoadjacent indicating sections, each section being marked with a series ofprogressively varying percent rates and having a principal valuedesignation part and a series of individual view openings alignedrespectively with the percent rate markings, said openings being in steparrangement, the percent rate markings on said two sections being thesame as to values and progression and the step arrangement of the Viewopenings in said two sections being similar; guide lines on said shieldextending respectively between and denoting two view openings in therespective sections aligned with equal percent rate markings; a nrstcylinder mounted to rotate behind one of said indicating sections andbeing marked with a circumferential column of primary principal valuesadapted to register with the principal value designation part of saidone of said indicating sections, and being also marked withcircumferential columns of primary percentages of said primary principalvalues adapted to be displayed through the openings aligned with thepercent rate markings on said one of said shield sections; and a secondcylinder mounted coaxially with said rst cylinder to rotateindependently oi said rst cylinder and behind the other of saidindicating sections and being marked with a circumferential column ofsecondary principal values and being also marked with circumferentialcolumns of secondary percentages of said secondary principal valuesadapted to be displayed through the openings aligned with the percentrate markings on said other of said indicating sections.

'7. In a percentage computation aid apparatus, a cylinder provided witha circumferential column of principal value markings; a series ofseparate annular sleeves mounted coaxially on said cylinder in end toend relation and being respectively marked with percentages, saidannular sleeves being mountable on and demountable from said cylinder bymovement axially of the cylinder; and cooperating means on the cylinderand sleeves respectively for maintaining said sleeves in predeterminedposition circumferentially with respect to said cylinder.

8. In a percentage computation aid apparatus, a cylinder provided with acircumferential column of principal value markings; a series of separateannular sleeves mounted on said cylinder and being respectively markedwith percentages, said annular sleeves being mountable on anddemountable from said cylinder by movement axially of the cylinder; andinter-engaging corrugations in the cylinder and sleeves respectively formaintaining said sleeves in predetermined position circumierentiallywith respect to said cylinder.

9. In a percentage computation aid apparatus, a fixed shield comprisingtwo adjacent indicating sections each marked with a series ofprogressively varying percent rates and having a principal valuedesignation part and a series of view openings aligned respectively withthe percent rate markings, said openings being in step arrangement, thepercent rate markings on said two sections being the same as to valuesand progression and the step arrangement of the view openings in saidtwo sections being similar; a rst member mounted to move behind one ofsaid indicating sections and being marked with a column of primaryprincipal values adapted to register with the principal valuedesignation part of said one of said indicating sections, and being alsomarked With columns of primary percentages of said primary principalvalues adapted to be displayed through the openings aligned with thepercent rate markings on said one of said shield sections; a secondmember mounted to move behind the other of said indicating sections andbeing marked with a column of secondary principal valuesY and being alsomarked with columns of secondary percentages of said secondary principalvalues adapted to be displayed through the openings aligned with thepercent rate markings on said other of said indicating sections; and ascreen mounted in iront of said movable members to move in the samegeneral direction as said movable members move, said screen having slotmeans extending transversely to said columns and being adapted toregister simultaneously with two selected view openings in therespective indicating sections aligned with equal percent rate markings,the non-slotted portion of said screen cutting off the view through theopen openings of the percentage Value columns behind said otheropenings.

10. In a percentage computation aid apparatus, a xed shield comprisingtwo adjacent indicating sections each marked with a series of alignedprogressively varying percent rates and having a principal valuedesignation part and a series of view openings aligned respectively withthe percent rate markings transversely to the Valignment of the markingsof said series, said openings being in step arrangement and atprogressively varying distances from the percent rate markings withwhich they are respectively aligned, the percent rate markings on saidtwo sections being the same as to values and progression and the steparrangement of the view openings in said two sections being similar; arst member mounted to move behind one of said indicating sections andbeing marked with a co1- umn ci primary principal values adapted toregister with the principal value designation part of said one of saidindicating sections, and being also marked with columns ofprimarypercentages of said primary principal values adapted to bedisplayed through the openings aligned with the percent rate markings onsaid one of said shield sections; a second member mounted to move behindthe other of said indicating sections and being marked with a column ofsecondary principal values and being also marked with columns ofsecondary percentages of said secondary principal values adapted to bedisplayed through the openings aligned with the percent rate markings onsaid other of said indicating sections; and a screen mounted in front ofsaid movable members to move in the same general direction as saidmovable members move, said screen having slot means extendingtransversely to said cohunns and beingV adapted to registersimultaneously with two selected view openings in the respectiveindicating sections aligned with equal percent rate markings, thenon-slotted portion of said screen cutting oir the View through theother openings of the percentage value columns behind said otheropenings, all of said columns extending transversely to said series ofaligned percent rates.

Y Vl1. In a percentage computation aid apparatus,

Va xed shield comprising two'adjacent indicating sections each markedwith a series of progressively varying percent rates and having aprincipal value designation part and a series of view openings alignedrespectively with the percent rate markings, said openings being in steparrangement, the percent rate markings on said two sections being thesame as to values and progression and the step arrangement of the viewopenings in said two sections being similar; a iirst cylinder mounted torotate behind one of said indicating sections and being marked with acircumferential column of primary principal values adapted to registerwith the principal value designation part of said one of said indicatingsections, and being also marked with circumferential columns of primarypercentages of said primary principal values adapted to be displayedthrough the openings aligned with the percent rate markings on said oneof said shield sections; a second cylinder mounted coaxially with saidrst cylinder to rotate independently of said first cylinder and behindthe other of said indicating sections and being marked with acircumferential column of secondary principal values and being alsomarked with circumferential columns of secondary percentages of saidsecondary principal values adapted to be displayed through the openingsaligned with the percent rate markings on said other of said indicatingsections; and a screen mounted in front of said cylinders to move in thesame general direction as said cylinders move, said screen having slotmeans extending transversely to said columns and being adapted toregister simultaneously with two selected view openings in therespective indicating sections aligned with equal percent rate markings,the non-slotted portion of said screen cutting oi the View through theother openings of the percentage value columns behind said otheropenings.

12. In a percentage computation aid apparatus, a centrally disposedsupport; a transverse mounting member carried by said support andprotruding therefrom to form oppositely disposed, coaxial bearingmembers; a primary principal value and percentage computation unitrotatably mounted on one of said bearing members; a secondary principalvalue and percentage computation unit rotatably mounted on the oppositebearing member, independently of said first unit; each of said unitscomprising a cylinder, marked with a circumferential column to representparts of principal values and adapted to be combined with markings ofthe corresponding columns of the opposite unit to collectivelyconstitute selected principal values, and a series of circumferentialcolumns representing percentages of the respective parts of theprincipal values and adapted to be combined with corresponding columnsof the opposite unit to collectively constitute complete percentages ofselected principal values; a common shield carried by said support andoverlying adjacent portions of the peripheries of said units; saidshield comprising two adjacent indicating sections, each marked with aseries of aligned progressively varying percentage rates and having aprincipal value designation part and a series of individual viewopenings aligned respectively with the percentage rate markingstransversely to the alignment of the markings of series, said openingsbeing in step arrangement and at progressively varying distances fromthe percentage rate markings with which they are respectively aligned;and guide lines on said shield extending respectively between and de- 13noting two view openings in the respective sections aligned with equalpercentage rate markings to facilitate the collective relating ofmarkings of the two cooperating units.

13. In a percentage computation aid apparatus, a iixed shield comprisingtwo adjacent indicating sections each marked with a series ofprogressively varying percent rates and having a principal valuedesignation part and a series of view openings aligned respectively withthe percent rate markings, said openings being in step arrangement, thepercent rate markings on said two sections being the same as to valuesand progression and the step arrangement of the view openings in saidtwo sections being similar; a rst member mounted to move behind one ofsaid indicating sections and being marked with a column of primaryprincipal values adapted to register with the principal valuedesignation part of said one of said indicating sections, and being alsomarked with columns of primary percentages of said primary principalvalues adapted to be displayed through the openings aligned with thepercent rate markings on said one of said shield sections; a secondmember mounted to move behind the other of said indicating sections andbeing marked with a column of secondary principal values and being alsomarked with columns of secondary percentages of said secondary principalvalues adapted to be displayed through the openings aligned with thepercent rate markings on said other of said indicating sections; ascreen mounted in front of said movable members to move in the samegeneral direction as said movable members move, said screen having slotmeans extending transversely to said columns and being adapted `toregister simultaneously with two selected view openings in therespective indicating sections aligned with equal percent rate markings,the non-slotted portion of said screen cutting off the View through theopen openings of the percentage value columns behind said otheropenings, a peripheral slot in said shield, and a radially projectingbutton on said screen, extending through said slot for manipulating saidscreen.

JOHN R. SEARS.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date 675,341 Rice May 28, 1901 698,141Roegner Apr. 22, 1902 760,360 Wiley May 17, 1904 896,710 Burhans Aug.25, 1908 914,439 Meilicke Mar. 9, 1909 1,127,492 Musgrove Feb. 9, 19151,360,726 Crook Nov. 30, 1920 FOREIGN PATENTS Number Country Date 25,345Great Britain 1912 40,982 Denmark Oct. 28. 1929

